Update TreeView's TvnEndLabelEdit method to set label to null when no text has changed (#13588)

* Update TreeView's TvnEndLabelEdit method to set label to null when no text has changed

Author: LeafShi1

src/System.Windows.Forms/System/Windows/Forms/Controls/TreeView/TreeView.cs

@@ -2575,10 +2575,6 @@ private LRESULT TvnBeginLabelEdit(NMTVDISPINFOW nmtvdi)
         if (!e.CancelEdit)
         {
             _editNode = editingNode;
-        }
-
-        if (!e.CancelEdit)
-        {
             _labelEdit = new TreeViewLabelEditNativeWindow(this);
             _labelEdit.AssignHandle(PInvokeCore.SendMessage(this, PInvoke.TVM_GETEDITCONTROL));
         }
@@ -2604,7 +2600,10 @@ private LRESULT TvnEndLabelEdit(NMTVDISPINFOW nmtvdi)
 
         TreeNode? node = NodeFromHandle(nmtvdi.item.hItem);
         string newText = nmtvdi.item.pszText.ToString();
-        NodeLabelEditEventArgs e = new(node, newText);
+        string? editedText = null;
+        if (node is not null && newText != node.Text)
+            editedText = newText;
+        NodeLabelEditEventArgs e = new(node, editedText);
         OnAfterLabelEdit(e);
         if (newText is not null && !e.CancelEdit && node is not null)
         {